Asymmetric Digital Subscriber Line (ADSL) is a technology which allows for simultaneous voice and data traffic to coexist over a communication channel comprising a standard telephone transmission line. Typically, the standard telephone transmission lines comprise an unshielded twisted pair of copper wire having a gauge of 22-26AWG. Twisted pairs, which can be used to connect a central telephone system (a `central` unit) to a subscriber's telephone (a `remote` unit) can support bandwidths of up to 2 MHz through the use of digital signal processing (DSP) technology. Thus, they can be used for bandwidth-intensive applications, such as internet access and video-on demand, as well as for carrying voice traffic. Frequency division multiplexing is used so that a plurality of signals, each occupying a different frequency band, can be simultaneously sent over the same transmission line.
The voice traffic band comprises a number of frequency sub-bands, or channels, ranging from DC to 20 KHz. The analog voiceband frequency is typically specified as 200-4000 Hz. Customer specified additions may include phone operation up to 8 KHz and 12-16 KHz billing tones. In addition, DC to 30 Hz frequencies are typically assigned for auxiliary analog signaling purposes, such as ringing the telephone, dial pulsing and on/off hook signaling.
ADSL data traffic bandwidth for CAP (carrierless amplitude and phase) modulation is typically from 35 KHz-1.5 MHZ. Of this, upstream data traffic (i.e., remote unit to central unit) uses the 35 KHz-191 KHz band, while the downstream traffic (i.e., central unit to remote unit) uses the 240 KHz-1.5 MHZ band.
Before providing the customer with ADSL service, the telephone company ("TELCO") must determine whether the line is suitable for ADSL communication. This is typically done by testing the lines between the TELCO's central office or substation, and the customer's site. In cases where the ADSL service is provided to the customer's residence, this often means testing the line at the point of entry to the building in which the customer's dwelling is located. After initiation of ADSL service, there are occasions in which the customer experiences problems in ADSL communication. In those instances, then TELCO must determine whether the trouble lies with the TELCO's equipment or with the customer's equipment. To make this determination, a TELCO representative may visit the customer's site to test whether the twisted pair line from the customer's site to the TELCO central office or substation is working properly, and also to test whether the customer's equipment is working properly. This requires considerable expense due to the time taken by the repairman.